Cross-sectional schematic of samples A and B.
TOF-SIMS Mg profiles of samples A (a) and B (c). In (b) and (d), the Mg content of the individual sublayers extracted from the Mg profiles (red lines in (a) and (c)) is plotted as a function of the Mg flux during growth. The red solid lines represent linear fits to the data. AFM images of the surface morphology are shown as insets and the rms roughness is indicated.
Reciprocal space maps of the 205 reflex of samples A (a) and B (b). The straight lines indicate the variation of the Zn1− x Mg x O peak position for pseudomorphic and fully relaxed growth, respectively. The dashed line represents partial relaxation with a degree of relaxation of R = 0.25.
Temperature-dependent PL spectra of samples A (a) and B (b). While the emission of the narrow well is blueshifted with respect to bulk ZnO and stable up to room temperature (a), the emission of sample B is redshifted due to the QCSE and rapidly quenches with increasing temperature.
Overview of parameters characterizing the SQW PL emission of samples A and B extracted from the temperature-dependent PL spectra shown in Fig. 4. The filled circles refer to the emission line related to free excitons for sample A, the open circles to donor-bound excitons of sample A, and the open diamonds to the SQW emission of sample B. The dashed lines represent least square fits according to Eqs. (1), (2), and (3), and Eq.(1) of Ref. 26, respectively. (a) Variation of the SQW PL peak positions with temperature. The crosses mark the energy position of the convoluted peak (BX + FX) of sample A. (b) Arrhenius plot of the integrated SQW PL intensity of samples A and B. The maximum value has been normalized to 1. (c) Temperature dependence of the FWHM of the SQW PL peaks.
(a) Power-dependent PL spectra of sample B at 4.2 K and (b) depiction of the PL peak shift. Due to the screening of polarization-induced interface charges for higher excitation power the SQW peak shifts to higher energies.
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